Mystery oil leak

XJ40
1

Kind of an odd problem on my XJS that may be better addressed here in the XJ40 forum. My 1994 XJS is a late 4.0L AJ6 version (Feb, '94) with 110K miles. Not your traditional oil leak that starts out slowly and then it gets worse as days go by. This leak started rather suddenly out of the clear sky the other day in my garage, about 3 to 4 minutes after I started out the engine, then it looked like if I let the engine run for a while the leak would become a puddle pretty soon. Now this repeats every time I start the engine, so for all purposes the car is down. However, no oil leak at all with the engine off.

The point where the oil drops to the ground is at the point where (on my ’94 XJS) the rear of the two catalytic converters (RCC) joins the rear exhaust manifold (REM). When I stop the engine to inspect the area I do see the bottom area of the REM somewhat humid from oil and down to the joint with the RCC. However, when I try to see where exactly this oil is emanating from I cannot see oil coming out from anywhere, besides, soon enough the REM gets hot, and smoke gets in the way. Based on gravity, I see no oil-wet metal anywhere above the REM, and neither any oil leaks from the cam cover joint/gasket above it; that cam cover seal joint is all dry. It’s like if the oil was coming out from inside the REM, but I can’t see how that could happen. I think the best would be to put the car on the lift, running, and to observe from underneath where can this oil possibly be coming out of before the heat burns it into smoke.
It seems like the XJ40 forum may have more AJ6 engine owners than the XJS forum, so I should be in the right place here. Tips welcome!
Cheers,

2

Hi I can’t offer any insight other than to say you are correct in that it is very unusual for an oil leak to be on that side of the engine, had it been from the front of the engine Exh side I would have guessed at the head gasket above the dizzy.
I do recall my father (long gone from this mortal life) relating how way back in the early part of the last century they had a vehicle that was spraying a VERY fine line of oil, they ended up holding a piece of paper and slowly approaching the leak that way to determine the actual point of egress.
Sounds like the hoist is the next best option.

3

The first thing I’d check is the D shaped seal that forms part of the cam cover seal arrangement, even if the gasket looks good all the way around it can still leak from that D seal at the rear. Check all of the screws that hold the cam cover on. The washers on the screws can become brittle and crack into several pieces over time, this actually happened to my car last year. The screws can feel tight enough when you try them but they won’t be doing a proper job of clamping the cover down evenly all round.

There is a cover plate on the rear of the cylinder head held in place with four bolts, I remember reading a post from another forum member who had a leak from that plate. It is difficult to see and to access, maybe a mirror on a stick might help you to inspect that area.

Other than those two areas I can’t think of anywhere else above the manifolds on the left side of the engine that oil could escape from as fast as it is.

Whatever it turns out to be, I hope you sort it soon.

4

Thanks for the responses.
Well, today we put the kitty up in the lift and in a few minutes (running) oil began to drip (however, very, very little this time) from the same previously described point, No oil coming out from absolutely nowhere else, meaning there’s no leak source other than, somehow, from the engine internals out to the exhaust manifold. Absolutely nothing coming out at any point around the cam cover, period, so the D seals do not appear to be an issue in this case.

Question is, how is this oil being thrown into the exhaust manifold (EM) and where from? I mean, the only source to the EM is the cylinder chamber(s) via the exhaust valve(s), but in that environment the temperature is just too high for any oil to remain in liquid form and just quietly reach the drip off point in the EM, as it would rather get burned before it can reach that drip point.

I’m no engine expert, so I ask, is there an alternate route for this oil to be pushed out if there was a fault in the head gasket? The only problem with that theory, however, would be that the exhaust port out to the EM is on the side of the head, so clearly ABOVE the head gasket, in which case the oil would need to defy gravity to travel upwards from the head gasket point towards the exhaust exit and still arrive there in liquid form.

So, no conclusions, other than possibly an internal engine failure, We cleaned dry the area real good where oil was present and judging from how smaller the leak was today at the shop, I decided to just drive the car back home (only five miles) to see what could possibly happen in stop and go 5:00 PM Friday night traffic, maybe it’d smoke like a locomotive, but here comes the funny part. I saw no smoke anywhere during the drive and to my surprise, when I got to my garage at home and opened the bonnet with a flash light in my hand… the exhaust manifold was still perfectly dry just like we cleaned it back at the shop, unbelievable. Later, I started the engine again and still no oil leak. I don’t know what to think because on the lift at the shop there already was significantly less oil coming out, how can the problem fix itself? I went from depression from knowing my kitty, perhaps, had cancer to the joy of seeing again its glorious looks healthy (really?) I wish I understood what was, and is, going on in there. Why was it leaking and why did it stop, even if it is only temporary. I guess that I’ll keep driving it in short stints at a time and just keep my fingers crossed. The drive felt so smooth and fun that I was well determined to resolve this one way or another.

Cheers,

5

I’m pleased to hear the leak seems to have stopped. Has the oil level on the dipstick remained constant since you drove the car back home from checking it on the lift ?

Is it possible the engine was overfilled with oil at some point ?

Was the car blowing out smoke from the tail pipes at the time when you first noticed the oil leak, or any oil dripping from the tail pipes ?

6

That was a thought that crossed my mind, we borrowed a Volvo from my brother in the UK many years ago and I over filled the oil prior to our tour. The car didn’t do anything silly but it did slowly reduce the level until it was at the top mark. It stayed there for the rest of the trip. Go figure?

7

Are you sure it was engine oil,

My XJSs were RHD but my LHD X300 has the power steering reservoir and various hoses for steering and coolers on the exhaust side. One of those might squirt onto the exhaust?

8

Casso, no, it never occurred to me to check the oil level since I had it changed by so-called professionals (about 300 miles ago, along with new brakes and new tires all around by a -supposed- reputable place). You hit the nail right in the head. I just checked the COLD oil level and it is about 1/2" higher than it is supposed to be. Why didn’t it show anything since the oil change, I don’t know, but I never saw oil in the garage floor before and no smoke at all. Well, I always wondered why they insist so much in not overfilling the oil, now I know.

If this is, indeed, going to be the end of this story, it sure is a happy ending because, with no other apparent or obvious issues, the excess oil surely jumps up to a clear #1 suspect and it represents no mechanical failures, thank God. Heck, I had already been checking prices for used engines, a thought that I hated because my AJ6 has a newly refurbished head, along with no less than a PORT AND POLISH JOB done by a race shop at the Las Vegas Motor Speedway Mall. You don’t want to let that beauty go in a trade deal just like that, unless I could keep it

Now I feel that, in regards to running gear, I’m better off coming to the XJ40 section with my AJ6 XJS.
Thank you all!

9

Not to be alarmist, but…

Check your coolant level, and do a compression test.

It might be a failed head gasket dumping coolant into the sump.

10

Robin, meaning that you didn’t see any oil dripping or smoking in the Volvo, period?
If you’ve read my previous post a little while ago you know I found the overfill issue. When I checked my cold oil this morning and before wiping the stick clean to do the check, it was completely oil-wet all the way to the top, as ready to start overflowing from the top of the stick well (when it was running, of course). I’ve seen this before in other cars, but never all the way to the top.

I’ll start driving this car around often enough to wear the oil down, hoping that it won’t drip anymore.
Thank XJ40 guys!

11

Reinaldo, no it slowly devoured the oil without any excessive smoke nd zero oil drips. As an aside, the brother was quite apologetic about the fact that at the time the car was about 10 years old. I think he may have felt better when I said that non of my cars in NZ were younger than 20yrs old.

12

Andrew, miles wise, that work on my AJ6 head was done a little less than 3,000 miles ago and it included a special heavy duty head gasket that was recommended by the racing people next door to them because, at that time, installation of a turbo on my XJS was being seriously considered, in which case a heavy duty gasket was a must.

Actually, I just went and gave it at least a quick visual check. The coolant level is perfectly where it is supposed to be, about 1/2" above the sensor and about an inch below the neck, beautiful, perfectly clean fluid. I carefully checked the oil throughout the stick for flaws, bubbles, etc. and it looks perfectly clean, in fact still fairly new, semi-transparent and without much brown in it.

I did accelerate the engine hard a few times on my way back from the shop, just to see if anything would “give up” and show damage signs, but everything went normal, including generous pull power from enhancements. I may still check compression, but if I keep driving it around and oil no longer leaks, or smokes and the coolant and oil integrity remain normal, then clearly, the whole thing was caused by an oil overfill.

Thank you!

Reinaldo

13

Peter, absolutely, it was engine oil. Verified it when I wiped it off the garage floor with white paper towel.
Cheers,